Over the past decade, several proposals to harmonize U.S. patent law with the rest of the world’s patent laws have been successful. The resulting amendments have changed many substantive rules of patent law in the United States, including novelty and loss of rights provisions, confidentiality of pending applications and term length. There is, nonetheless, one rule of patent law in the United States that has repeatedly withstood proposals for amendment, beginning at least in the 1960s and continuing through 2005: the first-to-invent rule of priority. On what seems to be the eve of its demise, this article maps out the extraordinary history of this singular American institution.